1. Field of the Invention
The present invention relates generally to desalination and more specifically it relates to a coal bed methane wastewater treatment system for efficiently and cost effectively treating wastewater generated from coal bed methane production.
2. Description of the Related Art
Coal bed methane (CH4) production has increased greatly since 1987. Methane is a flammable gas (the major constituent of natural gas) trapped in coal fractures by water. When a well is drilled into the coal formation and the water is extracted, the trapped methane gas can also be recovered. Existing coal bed methane wells are producing millions of cubic feet of coal bed methane (CBM), but are also producing millions of gallons of CBM wastewater.
While CBM wastewater (CBMW) is suitable for domestic and stock use, it is generally toxic to plants and crops. CBMW can come from as deep as 700 feet below the surface, and generally contains high concentrations of dissolved salts (e.g. sodium, bicarbonate), making it unsuitable for irrigation. The ratio of dissolved salts (referred to as the sodium absorption ration, or SAR) of CBMW is many times the level native plants and most crops can tolerate. Soil irrigated with CBMW will accumulate these salts, which destroys soil structure and inhibits water absorption by plants.
Surface discharge to natural waterways is the easiest and most economical method of disposing of the CBMW. However, since CBMW has high levels of sodium and bicarbonates, severe environmental concerns have been raised (e.g. wildlife, plants, environment, etc.). Hence, discharging untreated CBMW directly into a natural waterway is not a feasible option.
Another method of treating CBMW is the usage of large wastewater impoundments (a.k.a. “holding ponds”, “infiltration ponds”, “zero discharge ponds”) within the ground surface that receive large volumes of CBMW. The CBMW within the impoundments eventually evaporates and filters into a shallow aquifer within the ground. The main problem with wastewater impoundments is that large acreages of land are required for this process. Another problem with wastewater impoundments is that the impoundments become contaminated with large amounts of sodium. Another problem with wastewater impoundments is that valuable quantities of water are lost to evaporation and shallow aquifers that are easily contaminated.
Another method of treating CBMW is to inject the CBMW back into an aquifer. While this approach avoids surface discharge, there is the potential for contamination of valuable aquifers and other environmental concerns.
Another method of treating CBMW is through conventional reverse osmosis or salt precipitation with an evaporation process that leaves the salt behind and traps the evaporated water. Conventional reverse osmosis is expensive and cost prohibitive with respect to CBMW. Evaporation and salt precipitation treatment is also not economical nor feasible with the large quantities of saline CBMW. Hence, there is a need for a CBMW treatment system that is efficient and cost effective.
While these devices may be suitable for the particular purpose to which they address, they are not as suitable for efficiently treating wastewater generated from coal bed methane production. Conventional CBMW treatments are inefficient and are costly to operate.
In these respects, the coal bed methane wastewater treatment system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of efficiently treating wastewater generated from coal bed methane production.